Successful organ transplantation requires effective physiological and pharmacological intervention of the immune system of an organ recipient. Immunologic mechanisms are universal among the human species. But histocompatibility variations between donor and recipient lead inevitably to rejection of donor tissue by stimulation of the recipient's immune system except, perhaps, in donor-recipient pairing of the monozygotic type. One approach to intervention of immune response in an organ transplant recipient, especially a recipient targeted for an allogenic or homologous graft, is by the use of immunosuppressive drugs. These drugs have been used to prolong survival of transplanted organs in recipients in cases involving, for example, transplants of kidney, liver, heart, bone marrow and pancreas.
There are several types of immunosuppressive drugs available for use in reducing organ rejection in transplantation. Such drugs fall within three major classes, namely: antiproliferative agents, antiinflammatory-acting compounds and inhibitors of lymphocyte activation.
Examples of the class of antiproliferative agents are azathioprine, cyclophosphamide and methotrexate. The compound azathioprine acts by interrupting DNA synthesis through inhibition of purine metabolism. The compound cyclophosphamide is an alkylating agent which interferes with enzyme actions and nucleotide crosslinking. The compound methotrexate is a folic acid antagonist which interferes with nucleotide synthesis. While drugs of the antiproliferative class may be effective immunosuppressives in organ transplant recipients by limiting cell proliferation, these drugs which mediate mitosis and cell division have severe side effects on normal cell populations which have a high turn-over rate, such as bone marrow cells and cells of the gastrointestinal (GI) tract lining. Accordingly, such drugs often have severe side effects, particularly, bone marrow depression, liver damage, hair loss and GI tract disturbances.
A second class of immunosuppressive drugs for use in transplantation is provided by compounds having antiinflammatory action. Representatives of this drug class are generally known as adrenal corticosteroids and have the advantage of not exerting globally systemic cytotoxic effects. These compounds usually act by inhibiting T-cell proliferation, or by reducing IL-2 production, or by reducing chemotaxis, or by reducing neutrophil or macrophage activity. Typical examples of adrenal corticosteroids are prednisone and prednisolone. Compounds of this class are sometimes used in combination with cytotoxic agents, such as compounds of the antiproliferative class because the corticosteroids are significantly less toxic. But the adrenal corticosteroids lack specificity of effect and can exert a broad range of metabolic, antiinflammatory and auto-immune effects. Typical side effects of this class include increased organ-recipient infections and interference with wound healing, as well as disturbing hemodynamic balance, carbohydrate and bone metabolism and mineral regulation.
A third class of immunosuppressive drugs for use in organ transplantation is provided by compounds which generally prevent or inhibit lymphocyte activation. Such compounds usually act by blocking activated T-cell proliferation, or by inhibiting IL-2 production, or by inhibiting lymphokine production which depresses B-cell and macrophage actions. The cyclosporin family of compounds is the leading example of drugs in this class. Such compounds are fungal metabolites which have been found to be very effective in suppressing helper T cells so as to reduce both cellular and humoral responses to newly-encountered antigens. Cyclosporins alter macrophage and lymphocyte activity by reducing lymphokine secretion and, in particular, by interfering with activation of antigen-specific CD-4 cells, by preventing IL-2 secretion and secretion of many T-cell products, as well as by interfering with expression of receptors for these lymphokines. Cyclosporin A, in particular, has been used extensively as an immunosuppressor agent in organ transplantation. Other microbial metabolites include cyclosporins such as cyclosporin B and cyclosporin G, and another microbial product known as FK-506. Cyclosporin A suppresses humoral immunity as well as cell-mediated reactions. Cyclosporin A is indicated for organ rejection in kidney, liver, heart, pancreas, bone-marrow and heart-lung transplants. Cyclosporin A is also useful in the treatment of autoimmune and inflammatory diseases, including rheumatoid arthritis, Crohn's disease, Graves ophthalmopathy, severe psoriasis, aplastic anemia, multiple-sclerosis, alopecia areata, penphigus and penphigoid, dermatomyositis, polymyositis, Behcet's disease, uveitis, pulmonary sarcocidiosis, biliary cirrhosis, myasthenia gravis and atopic dermatitis.
Cyclosporins do possess several significant disadvantages. Firstly, while cyclosporins have provided significant benefits in organ transplantation, cyclosporins are non-specific immunosuppressives. Thus, immunologic reactions to transplanted tissue are not totally impeded, and desirable immune reactions may be reduced against other foreign antigens. Secondly, cyclosporins can produce severe side effects in many organ recipients. And cyclosporins show host-variable effects on the liver, the CNS and GI tract. Significant among the adverse side effects are damage to the kidney and hyperplasia of gum tissue.
Thus, the need remains for efficacious, selective immunosuppressive drugs in organ transplantation, especially for grafts between less-than-perfectly matched donor-recipient pairs.
Phenylacetonitrile compounds are known for use in treatment of cardiovascular diseases. For example, U.S. Pat. No. 3,261,859 describes phenylacetonitrile compounds, including the well-known compound verapamil, for use as coronary dilators. U.S. Pat. No. 4,593,042 describes certain bicycloamino-substituted phenylacetonitrilealkyl compounds, including several specific compounds having an isopropyl group attached to the alkylene alpha carbon of the phenylacetonitrile nucleus. Such compounds are characterized as calcium ion blockers for use in treatment of hypertension. U.S. Pat. No. 4,681,970 describes bicycloamino-substituted phenylacetonitrilealkyl compounds, several specific compounds of which have a long chain alkyl group (i.e., twelve carbons) attached to the alkylene alpha carbon of the phenylacetonitrile nucleus. These compounds are characterized as calcium channel blockers for treatment of hypertension.
Phenylacetonitrile compounds have been investigated for other pharmaceutical purposes. For example, certain calcium channel blocking agents, including verapamil, have been investigated for antiproliferative effects on T-cell mitogenesis [G. Walz et al, Transplantation, 47, 33-334 (1989)]. Various calcium channel blockers, including verapamil and nifedipine, have been studied for interaction with stimulated T-lymphocytes [A. Nell et al, Scan. J. Immunology, 24, 283-290 (1986)]. German Offen. 3826796 published 8 Feb. 1990 describes substituted phenylacetonitrile compounds for use in overcoming resistance to antimalarial or anticancer agents. The calcium antagonists verapamil, nifedipine and nicardipine were compared and found to produce dose-dependent acute and chronic antiinflammatory effects [W. R. Chen et al, Acta. Pharmacologica Sinica, 11 (3), 281-285 (1990) ].